The present invention relates to a method and apparatus for the removal of obstructions, deposits and/or other debris from pipelines, wellbores and other confined areas. More particularly, the present invention relates to a method and apparatus for use of continuous tubing to remove obstructions restricting or completely preventing flow in pipelines or well bores including, without limitation, stuck pigs, hydrate plugs, scale, paraffin and/or other debris.
As known deposits of oil and gas become depleted, exploration for new deposits must be undertaken in more remote locations. This is especially true with offshore oil and gas operations; many current exploration and development activities are conducted a great distance from land in deep water environments.
Many offshore wells, particularly wells drilled in deep water environments, are drilled and completed using floating drilling rigs, such as drill ships and semi-submersible drilling rigs. In such cases, wellhead assemblies are typically not located on a permanently anchored support structure or floating rig, but rather on the sea floor. As a result, specialized equipment known as “subsea” wellhead assemblies are utilized. In such cases, the subsea wellhead assemblies are situated on the sea floor, while pipelines are used to connect such subsea wellheads to one another and/or to surface facilities that gather and process production from the subsea wells. Additionally, larger pipelines are routinely used to gather production from multiple offshore installations and transport such production to shore.
As relatively hot hydrocarbons are produced from subterranean reservoirs up to wellhead equipment situated at the sea floor, and thereafter through pipelines extending along the sea floor, such hydrocarbons are cooled by the relatively low temperature of the surrounding water. Frequently, this cooling can occur rapidly, causing wax or paraffin present in hydrocarbons to solidify. Such solid materials can be deposited or “plated” on the internal diameters of such pipelines, restricting or clogging the flow bores in said pipelines and limiting passage therethrough.
A common treatment for the removal of deposits and/or other debris on the internal surfaces of pipelines involves the insertion of mechanical cleaning devices—commonly referred to as “pigs”—into the flow bores of such pipelines. Although such pigs have many different shapes and sizes, pigs are typically cylindrical or spherical tools that can be used to mechanically scrape paraffin and/or other debris from the internal surfaces of pipelines.
Frequently, as a pig passes through a pipeline and mechanically scrapes paraffin and/or other debris from the inner surfaces of such pipeline, the paraffin and/or debris can accumulate along the leading edge(s) of the pig. As such paraffin and/or debris collects, it can build up and restrict the internal opening of the pipeline, eventually forming an obstruction that can limit forward progress of the pig. This action can continue until fluid pressure behind the pig is no longer capable of forcing the pig through the line. Eventually, the pig can become stuck, such that it can not be moved by pressure from either direction, with the internal opening of the pipeline becoming fully obstructed.
In recent years, oil and gas operators have discovered an alternative to conventional rig operations that uses a length of continuous, flexible tubing rather than multiple sections of rigid pipe. This alternative, commonly referred to as “coiled tubing”, utilizes a continuous length (up to 10,000 feet or more) of flexible tubing which is stored on a reel. Such conventional coiled tubing can be partially unspooled from such reel and translated in and out of a wellbore in a virtually continuous manner without having to continually connect and/or disconnect individual pipe sections as with jointed pipe.
In recent years, continuous tubing has been beneficially used in connection with efforts to remove stuck pigs and/or other obstructions (including, without limitation, hydrate plugs, scale, paraffin or other debris) from pipelines. Such continuous tubing can be concentrically inserted into a pipeline and used to push or otherwise urge stuck pigs or other obstructions through the internal flow bore of a pipeline. Because the continuous tubing is relatively flexible, it can be rolled off a large reel (such as from a boat or other support structure) and into a pipeline. Further, multiple tubing strings can be joined together to allow for increased length, and tools or other beneficially-designed equipment can be attached to such continuous tubing in order to engage a pig or other obstruction in the pipeline.
Large forces are often required to force extended lengths of continuous tubing into a pipeline that may be filled with hydrocarbons, solid deposits and/or other materials. While conventional devices known as injector heads can be used to grip the continuous tubing and mechanically force it into the pipeline from the surface, such tubing can become bent, kinked or “corkscrewed” during this process. Furthermore, in the event that the continuous tubing enters a horizontal section of pipeline, the weight of the tubing can act against the internal surfaces of the pipeline, thereby creating frictional forces that impede the forward progress of the tubing through the pipeline. As a result, conventional injector heads and other similar devices have proven to be less than satisfactory for purposes of conveying continuous tubing within pipelines.
Other methods have been developed in an effort to increase the length to which continuous tubing can be injected into pipelines. For example, one such method entails utilizing a thruster device installed on the distal end of a section of continuous tubing, and utilizing a pressure differential across the thruster pig to generate force needed to advance the tubing within the pipeline. However, the subject thruster device is not capable of simultaneously advancing in the pipeline and cleaning away obstructions in said pipeline. Moreover, the thruster device will not allow pieces of debris to be circulated out of the pipeline behind the thruster device.
Thus, it is an object of the present invention to provide a method and apparatus for cleaning pipelines and removing stuck pigs at great distances (up to 10 miles and beyond) using continuous tubing. It is a further object of the present invention to safely extend the horizontal reach of continuous tubing in pipelines and/or other similar controlled environments, while permitting the use of down hole motors, bit slammers, fishing over-shots, memory tools and/or other conventional coiled tubing tools, including tools requiring internal flow actuation.
It is yet another object of the present invention to provide a method and apparatus for creating a jetting action in a pipeline at or near the distal end of a string of continuous tubing, while advancing such tubing forward to a desired location of a stuck pig or other restriction or obstruction within said pipeline.
It is yet another object of the present invention to provide a method and apparatus for providing a check valve system to permit the relief of compressed fluids as a stuck pig or other obstruction is speared or otherwise gripped using continuous tubing, as well as the removal of said pig or other obstruction.